The present disclosure will relate to the field of image stabilization, i.e. improvement of quality of a video image stream otherwise deteriorated by camera motion. There are numerous versions of digital-image stabilization, i.e. software applications that process stored image streams such that shakes or vibrations are minimized in a processed image stream. In the case of cameras, shakes or vibrations may be operator-induced or a result of a suspension not being able to suspend the camera in a vibration-free way. Solutions solely relying on a software-algorithm are often based on tracking of a finite number of features from image to image in the stream, and ensuring that these features are maintained static in a displayed image. These software solutions may be highly efficient in reducing the effect of shakes and vibrations, yet they may have a drawback in monitoring applications or surveillance applications where they may introduce an unwanted temporal lag, apart from consuming a significant computing power.
An alternative to this may be to use optical image stabilization, e.g. by shifting a set of lenses so as to shift an image parallel to the image plane and thereby counteracting the effect of the vibration or the shake. The shift of the set of lenses is performed as a response to a vibration quantified by miniature sensors, and it generally will require input of the focal-length settings. This technique may minimize the effect of a vibration or shake at the cost of a complex system. Also, the technique enables cancellation of blurring, otherwise being an effect of lens movement during exposure time.
Still another alternative may be to use a sensor-shift technology where the actual image sensor is shifted so as to follow the shift of the image induced by the motion of the camera.
The suggested methods all have their advantages and disadvantages. The present disclosure will mainly address issues appearing in relation to angular movement in a pan direction and/or a tilt direction. There are several aspects of this, yet for a monitoring camera or surveillance camera mounted in a fixed location and having pan/tilt functionality, a vibration in a pan/tilt dimensions may be a common effect during particularly windy conditions, as a result of heavy traffic, etc. The invention as disclosed herein may be applied to any video camera.
Some lenses uses feedback from zoom motors in order to keep track of the present focal length. However, there are also zoom lenses that do not have this feature, e.g. lenses where the zoom settings are made manually and other zoom lenses where there is no feedback function associated with the zoom motors. The category “zoom lenses” is typically divided into varifocal lenses and parfocal lenses and for the purposes of the present disclosure the word “zoom lens” will mainly be used and zoom setting and focus setting or focal length setting will be used in parallel.